Free PHP Image Manipulation Class – ImageWorkshop
ImageWorkshop is an open source and free PHP class for managing and manipulating images.
The class has an "image-editing-software-like logic" based on layers which enables superposing many layers or even layer groups (with the option of each layer being manipulated differently).
It has support for many functions like placing an image (or many images) on another one (good for watermarks), cropping, moving, resizing, rotating (with any degrees), superposing, writing and more.
ImageWorkshop works with the GD library, and also, allows us to apply filters provided with the library.